The present invention relates generally to chucks for use with hand or power drills or with electric or pneumatic power drivers. More particularly, the present invention relates to a chuck of the keyless type which may be tightened or loosened by hand or by actuation of the driver motor.
Both hand and electric or pneumatic tool drivers are well known. Although twist drills are the most common tools used with such drivers, the tools may also comprise screwdrivers, nut drivers, burrs, mounted grinding stones and other cutting or abrading tools. Since the tools may have shanks of varying diameter or the cross-section of the tool shank may be polygonal, the device is usually provided with a chuck which is adjustable over a relatively wide range. The chuck may be attached to the driver by a threaded or tapered bore.
A wide variety of chucks have been developed in the art. In the simplest form of chuck, three jaws spaced circumferentially approximately 120 degrees apart from each other are constrained by angularly disposed passageways in a body attached onto the drive shaft of a driver. The chucks are configured so that rotation of an internally threaded tightening ring or nut that mates with external threads on the jaws forces the jaws into gripping relationship with respect to the cylindrical shank of a tool when rotated in one direction, while rotation in the opposite direction releases the gripping relationship. Such a chuck may be keyless if it is rotated by hand. One example of such a chuck is disclosed in U.S. Pat. No. 5,125,673 entitled "Non-Impact Keyless Chuck" commonly assigned to the present assignee, and whose entire disclosure is incorporated by reference herein.
It is desirable in a keyless chuck to obtain a sufficient holding force within the tightening capability of a normal user. With many of the jaw type chucks as described above, one means of enhancing holding force on a tool has been to use relatively fine threads on the jaws that mate with the nut to enhance the amount of force that can be generated. This solution has the disadvantage that a relatively large number of turns of the nut are necessary to span the range of diameters of tools that can be accepted by the chucks. In addition, friction reducing means such as bearings have been utilized to further enhance the amount of tightening force than can be generated. Further, it may be desirable to enhance the gripping force obtainable by a normal user above and beyond what is now obtainable with currently available three-jaw chucks.